Question: Hello I was wondering have we ever received any radio signals from space? What I’m trying to ask has earth ever received a message from space? – Brandon
Answer: Well, in fact, all objects in the universe that emit electromagnetic radiation (or “light”) emit radio waves. Remember that “radio waves” are just one small chunk of what physicists call the “electromagnetic spectrum”. So, in a literal sense, the answer to your question is yes. I believe, though, that what you are really asking is if we have received an artificial radio signal from another civilization. The answer to that question is definitely no. That indeed would an event that we would all hear about!
Through a very interesting article in the latest edition of Astronomy Beat, produced by my colleagues at the Astronomical Society of the Pacific (ASP), I was re-introduced to a wonderful little PBS-produced television show called “Star Gazers”. These 5-ish minute episodes describing celestial events viewable by backyard astronomers were hosted by a guy named Jack Horkheimer from 1976 through 2010. Jack obtained a kind of cult following for these Star Gazer (actually, it was originally titled “Star Hustler”) episodes by his lovably eccentric yet comfortable style of describing the astronomy happening over our heads. Jack’s episodes are posted to YouTube (like most everything else), so you can get a sample of those classic shows.
The modern version of Star Gazers (note the subtle change in the title from its predecessor, as there are now three hosts for this show) is fantastic! I highly recommend it for those interested in finding out what astronomical events are taking place each week. You don’t need to be a degree-carrying scientist to understand the information presented in these episodes either. It is definitely a good use of five minutes each week!
Question: How many planets a stellar-planetary system can accommodate safely into a stable orbit around that star? What are the factors it depends on?
For Example: Currently our solar system has 8 planets in a stable orbit. I want to know the maximum possible number of planets our system can accommodate so that added planets(beyond the orbit of Neptune) also follow the orbital pattern of 8 existing planets?
Suppose all the planets in our solar system are exact replica like Earth, then how many earth-like planets that our current sun can get hold off? – Vinod
Answer: With no other constraints on the star or the planets that orbit the star, the only requirement for stable orbits of planets around the star is that the total mass of the planets be less than the mass of the star. Therefore, one could in principal have a nearly infinite number of very small planets that orbit a star. In reality there are other constraints, such as merging of small planets that are near each other in the early phases of the formation of a planetary system, that reduces the final configuration of a planetary system. These additional constraints, though, conspire in a complex way to produce the final orbital configuration for an exoplanetary system.
Question: I please was curious to ask about the VLA located between Datil and Magdalena, NM — is it true that the railroad equipment used to build the layout came from the Santa Fe Railway? – Lindsey
Answer: The original railroad ties used on the VLA transporter tracks came from old Department of Defense railroads in the 1970s. Today replacements are made with brand new ties.
Question: I am suspicious about Kepler’s area law. Such law should not exist. I am finding “the cycling velocity of the celestial body is constant and not the swept out area”. How to prove that area 1/2*r*Vp=constant? In addition I discover r*Vp^2=Constant where (r=distance to the sun; Vp=revolving velocity of the body around the sun). The data of the planets (r;Vp) confirm this constant,then if r*Vp^2=Constant,may not allow area r*Vp to be constant.
Here are some sample for r*Vp^2=1,32725E+11 km^3/sec^2
Earth r=149597890 km Vp=29,78607371 km/Sec
Mars r=227939150 km Vp=24,13051171 km/sec
You may use the known data to confirm r*Vp^2=CT.
Then how to prove Kepler’s are law r*Vp=Ct.That should be wrong — Necat
Answer: I think that your fundamental assumption, that the velocity of the celestial body is constant, is the part that is the source of confusion regarding Kepler’s second law. Let me point you to a very nice and detailed derivation of Kepler’s laws that explains both the math and the physics behind the proof of Kepler’s three laws. To summarize the derivation, you can show with a simple geometrical argument that the rate of sweeping out of area in the orbit of a celestial body is proportional to the angular momentum of the celestial body. Since Newton’s Laws tell us that the rate of change of angular momentum torque of the forces acting on the body, which is zero for celestial bodies orbiting a star like our Sun. Since the rate of change of angular momentum is zero, that angular momentum must be constant, which then says that the rate of change of swept-out area for the orbit of the celestial body must be constant. This then leads to Kepler’s Second Law, that celestial objects in orbit sweep out equal areas in equal time.
Question: What are the chances of interplanetary space crafts, probes and rovers carrying the air-borne bacteria and viruses and dispersing them in the target planet since they are made and assembled in earth? (Especially the rovers which landed on Mars and the Huygens probe which landed on Titan, since they are pristine planets devoid of any life forms and bacteria & viruses known survive in very extreme conditions contaminating those planets via probes). – Vinod
Answer: Scientists have been concerned about this issue since the early days of space exploration. There is a committee of scientists, called the Committee on Space Research (COSPAR), that develops recommendations for avoiding interplanetary contamination by space probes. The aim of the current regulations is to keep the number of micro-organisms on an interplanetary space probe low enough so that the probability of contamination of the target body to a level no greater than 1 in 10,000. The details of the rules governing the potential contamination by interplanetary space probes is described very nicely in the Wikipedia article on Planetary Protection.
Question: What is the difference between Doppler shift of light and Natural light spectra (blue for young and red for old) with respect to stars and galaxies? How does astronomers differentiate between Doppler shift and Natural light spectra of deep space objects?
For Example: Consider a deep space object which is actually young (blue color) and also receding away from earth but due to its enormous distance from earth it is red-shifted (appears as red-colored in Hubble observations) due to Doppler effect. In the above condition, how does an astronomer determine the true color of the cosmic body? – Vinod
Answer: The color of an object is determined by the peak in its continuum emission, which is itself determined by how hot the object is. For example, a star that appears red is colder than a star that appears blue. Redshift, on the other hand, is a property determined by the shift in wavelength of spectral lines emitted by the gas in an object. Now, a redshifted object will also have a redshifted peak to its continuum emission, so it also will appear redder. If we can measure the redshift of this object we can determine its true color by correcting for the reddening caused by high recession velocity.
Question: How can Hubble give pictures with different zoom levels? If telescopes are constructed with a fixed focal length and cannot “zoom”. How come that Hubble can see individual stars in the Andromeda Galaxy http://www.spacetelescope.org/images/heic1112a/. But can also see the whole galaxy http://www.spacetelescope.org/images/opo0315f/. – Nikola
Answer: Many telescopes, the Hubble Space Telescope being one of them, uses array detectors to capture the light from stars and galaxies. Array detectors are composed of individual pixels which determine the telescope’s ability to separate objects that are very close to each other or to detect objects that are very small. By putting many of these pixels together as an array, we can stitch together many pixels to make a picture, or “image” of larger objects while still retaining the ability to see small objects. This is how we are able to see both galaxies and the individual stars within those galaxies.
Question: How do you use a dish type radio telescope to produce an image of something occupying such a small fragment of the sky? – Martin
Answer: There are a couple of ways to make images of small objects using an array of radio telescopes. You need to connect the radio telescopes so that they act like an array. When radio telescopes make measurements together as an array, the resolution that the array can attain is determined by the largest distance between the individual antennas in the array. So, if we can move telescopes in an array as far apart as possible, we can make very high spatial resolution measurements. This is basically how we make high spatial resolution measurements of very small areas on the sky. A nice description of how a radio telescope and a collection of radio telescopes functioning as an array can be found on the Square Kilometer Array web site.
Question: Has radio astronomy (less than 100 years old) been able to detect change over time, other than regular periodic motion or oscillation? For example, the actual formation of a star, or a supernova, or gas or dust accretion? For example, before and after images that show significant change. Another way of asking: are the processes of change in the universe observed, or inferred? – Peter
Answer: Yes. The best example of a radio observation which tracks changes in the radio emission from an object is the measurements of the proper motions of water masers in star formation regions in our galaxy. Measurements over periods ranging from just a couple of years to 30 years have traced the motion of these signposts of shocked gas in star formation regions. Another example are the changes in radio emission from supernova remnants. The radio emission from the supernova remnant produced by the supernova 1987A over the period 1991 to 2013 has been quantified. These are just a few examples.